Composite structure

ABSTRACT

A composite web structure utilizing a thin first layer of material having a plurality of structural fibers arranged to lie essentially in a unidirectional orientation. A thin second layer of material is positioned adjacent the first layer and includes a plurality of structural fibers. First and second layers are impregnated with a matrix material for binding fibers within the first and second layers and for binding the first and second layers together. The web may be formed into a composite structure such as a honeycomb core for fabrication into a panel.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/688,063, now U.S. Pat.No. 5,730,920 filed Jul. 29, 1996.

BACKGROUND OF THE INVENTION

The present invention relates to a novel web and composite structureformed therefrom.

Composites are generally an assembly of dissimilar materials that worktogether to perform a function only possible in the composite form.Generally, composites include a resin matrix with a fiber reinforcementmaterial. "Advanced composites" generally refer to newer materialsforming the resin matrix or the fiber reinforcements in which the fiberspossess a Young's Modulus of greater than 12 million.

Fibers can be constructed of Kevlar, carbon fiber, Nextel, boron, or anyother materials having a very small diameter and high strength andstiffness. Resins may typically consist of an epoxy, polycyanate,bismaleimide, and the like. The strength and stiffness of the resinmatrix also affects the strength of the finished composite structure.For example, stronger resins such as epoxies usually yield a higherstrength composite structure than lower strength resins such aspolyester.

Structural fibers are generally formed into yarns or rovings whichinclude a number of twisted or untwisted strands either plied togetheror formed in a continuous filament. In the past, these yarns have beenwoven into a cloth entailing the application of a sizing or lubricant toachieve this condition. After weaving, the lubricant is removed and asurface finish is applied either to prevent or promote the adhesion ofresins which are later applied during the pre-impregnation or assemblyprocess. In this regard, reference is made to U.S. Pat. No. 4,534,919which discloses a carbon fiber tow suited for resin impregnation havingdisrupted parallel filaments.

Unidirectional tapes have been constructed of carbon fibers or otherfibers in a dry fiber form or in a form pre-impregnated with a resinmatrix. For example Y.L.A Inc. of Benicia, Calif. produces a single plyunidirectional tape under the designation XN 50A/RS-3. Suchunidirectional tapes have been used in layup processes for thefabrication of sporting goods and aeronautical structures such as wingskins, solar arrays in satellites and the like. Lack of transverseintegrity limits formation of core structures from existingunidirectional tapes, ie; they are delicate and prone to splitting alongthe side-by-side fibers. Thus, such unidirectional tapes are difficultto handle and process into a honeycomb structure.

Structural fibers may be formed into finished composite structureseither by employing woven or non-woven web reinforcing material. Forexample, U.S. Pat. No. 5,013,514 proposes production of a hollow elementutilizing woven or non-woven carbon fiber mats. U.S. Pat. No. 3,255,062shows a method of manufacturing a reinforced honeycomb structureutilizing foam, plastic, or cardboard. U.S. Pat. No. 3,200,489 teaches amethod of making a honeycomb core using stainless steel which isexpanded from multiple foils or sheets which are bonded together atpoints.

U.S. Pat. Nos. 3,248,275 and 3,137,604 describe a honeycomb structureformed of resins impregnated in glass cloth. U.S. Pat. No. 4,563,321reveals a method of producing a unitary curved structure having ahoneycomb core which employs woven fiber glass material and an outerlayer of chopped glass fibers.

The use of honeycomb core materials for constructing lightweight panelsor sandwich structures is well established in the aeronautical andspacecraft fields. For example, in commercial aircraft, nearly all ofthe movable control surfaces, wing and tail leading and trailing edgefixed surfaces, doors, and interior cabin structures employ panelsformed of honeycomb cores. Such prior art cores have typically beenconstructed of an aluminum or Aramid paper (known as Nomex) honeycomb.Although more expensive than simple structures, the honeycomb core panelpossess equal strength at higher stiffness, lower weight, and isresistant to higher natural vibration frequencies. Such resistance isvery important when structural elements are employed in close proximityto jet and rocket engines. Reference is made in this regard to treatisesentitled "Composite Basics", second edition by A. Marshall;International Encylopedia of Composities, Volume 1, pgs. 488-507, Lee;Handbook of Composites, chapter 21, G. Lubin; and a brochure entitled"Honeycomb, TSB 120", Hexcel Corp. which describe honeycomb cores indetail. Moreover, the honeycomb core must have small enough cell sizesto provide stabilization of the facings against premature buckling. Inaddition, the core must be sufficiently tough and abuse resistant toenable the same to be easily handled in a fabrication shop.

Aramid honeycombs are used where high damage tolerance and abuseresistance is a criteria. However, Aramid honeycombs lack the shear andcompressive strength of aluminum honeycombs.

Aluminum, the presently preferred core material for minimum weightprimary structures in spacecraft and aircraft, also possesses problemsin that using the same at one pound per cubic foot density providesample strength for the primary loading of a structure, but results in avery fragile structure which is easily damaged when subjected to thenormal manufacturing, assembling and testing procedures used infabrication. In addition, aluminum cores do not provide a compatiblecoefficient of thermal expansion relative to the facing material whichis normally a carbon fiber. As a result, changes in temperature resultin the warpage of the structure. Such warpage can occur during the panelmanufacturing process as a result of cool-down from the core-facingbonding temperature to room temperature, typically a 275 degreefahrenheit difference. Also, warpage occurs in outerspace if such apanel is employed as a spacecraft structure when the spacecraft movesfrom daylight to darkness and back again.

A lightweight, thin, web having unidirectional structural fibers forconstructing lightweight honeycomb cores would be a great advance in thefield of materials technology.

SUMMARY OF THE INVENTION

The present invention relates to a novel composite structure which isparticularly useful in forming a honeycomb core.

The composite structure of the present invention utilizes a first layerof material having a plurality of structural fibers arranged to liesubstantially unidirectionaly within the layer. In its preferredembodiment, the first layer of material is relatively thin, having athickness of only several fibers. The first layer may be composed offibers such as carbon fiber, Kevlar fiber, polyethylene terapthalatefibers (known as Spectra), and the like.

The composite structure also includes a second layer of materialpositioned adjacent the first layer which also includes a plurality ofstructural fibers. The structural fibers of the second layer may be ineither random configuration, or unidirectional configuration and mayconsist of a material which is the same or different from the materialof the structural fibers employed in the first layer. Where the fibersof the second layer are unidirectional, such fibers lie in a differentdirection than the fibers in the first layer, preferably at about 90°relative to the unidirectional fibers of the first layer.

The composite structure of the present invention also entails means forimpregnating the first and second layers with a matrix which binds thefibers within the first and second layers. Binding would alsoessentially connect the first and second layers to one another to form atwo-ply web or tape. Such means may include the use of a compatibleresin material for pre-impregnating both layers of material.

It should be further noted that the composite structure described hereinmay also include one or more additional layers of material having aplurality of structural fibers arranged in a substantiallyunidirectional orientation. The direction of the fibers in each of thenon-adjacent unidirectional layers may be coincident or non-coincident.In addition, the composition of the structural fibers in each of theunidirectional layers may be the same or different depending on theintended use of the composite structure. For example, a mixture of 75million psi modulus carbon fibers and 100 million psi modulus carbonfibers may be mixed in a single layer.

Such multilayer preimpregnated composite web may be formed into ahoneycomb core. Further, the unidirectional fibers may be positionedwithin the honeycomb and oriented in a direction which permitsside-by-side fibers to be located in the optimum direction to bearspecific loads applied to the honeycomb core. The resulting density ofsuch a honeycomb core is less than 2 pounds per cubic foot, andpreferably, less than 1 pound per cubic foot. In addition, preliminarytesting indicates that higher strength and stiffness is obtained at thesame or lower densities than is obtained by honeycomb cores producedwith woven fabrics employing identical fibers of aluminum foil.

The process for manufacturing such a honeycomb encompasses providing abase with a surface of geometrically predetermined facets for producinga particular honeycomb cell structure, eg; right regular hexagons,rectangles, circles and the like. Reference is made hereat to FIG. 21.8of the treatise Handbook of Composites previously cited. The facetedsurface is overlain with the prior described multi-ply web structure ofthe present invention having a first unidirectional layer and a secondlayer which may include fibers of random configuration, both layersbeing impregnated with resin material. A plurality of heat expansivemandrels are placed on top of the web structure over the recesses formedon the faceted surface of the base. Of course, the mandrels would beformed with a cross-sectional configuration matching the cell structurerequired on any particular honeycomb core. A second web or tapeutilizing the composite structure of the present invention is placedover the mandrels. Successive layers of tape and interleaved mandrelsare stacked to the desired width of the block or core. Sufficient heatand pressure are then applied to the multiple webs and mandrels to curethe block and for a composite structure. Pressure is either applied by avacuum bag or through the stacking and restraining of the mandrelswithin the core forming apparatus. After cooling, the mandrels areremoved from the multiple webs or tapes leaving a curved honeycomb core.It should be noted that the mandrels may be composed of a heatconducting material such a aluminum, copper, and the like, and may becoated with a material which prevents the mandrels from sticking to thehoneycomb core. In addition, the mandrels may be composed of a materialhaving a higher coefficient of thermal expansion (CTE) than the webmaterial, which aids in the application of pressure to the core duringthe curing process.

Moreover, the unidirectional fibers would all be oriented relative tothe thickness direction of the finished honeycomb core such that theoptimum performance of the honeycomb core is realized.

It may be apparent that a novel and useful web for use in a novelcomposite structure has been described.

It is therefore an object of the present invention to provide acomposite web which employs a first layer of unidirectional fibers and asecond layer of structural fibers which are fused to the first layer byan impregnating resin, permitting a multiply tape formed thereby topossesses stability and workability in the formation of complexcomposite structures.

It is another object of the present invention to provide a composite webwhich may be formed into a honeycomb which possesses lower density thanprior honeycombs formed of woven fabrics or aluminum, yet possessesusable strength and stiffness.

Another object of the present invention is to provide a composite webwhich may be formed into a honeycomb core which has a lower coefficientof thermal expansion than prior honeycombs formed from woven fabrics ormetal foils.

A further object of the present invention is to provide a composite webwhich may be formed into a honeycomb core whose coefficient of thermalexpansion may be set at a predetermined value.

Yet another object of the present invention is to provide a compositeweb which may be formed into a honeycomb core which is simple tocustomize for its intended use employing minimal tooling and, thus,reducing tooling costs.

A further object of the present invention is to provide a carbon fibercomposite web which may be formed into a honeycomb core having a higherthermal conductivity per unit weight than prior art carbon fiberhoneycombs.

Yet another object of the present invention is to provide a compositeweb which may formed into a honeycomb core which is easily processedinto a panel having less susceptibility to warpage than prior artaluminum honeycomb core panels of similar density.

Another object of the present invention is to provide a composite webwhich may formed into honeycomb core structures having modestcurvatures, including honeycomb core cell shapes known in the prior art.

Another object of the present invention is to provide composite webwhich may be formed into a honeycomb core that is resistant to naturalvibration frequencies produced by jet and rocket engines.

A further object of the present invention is to provide a composite webor tape having at least three layers, including unidirectional fiberlayers, to form composite structures.

The invention possesses other objects and advantages especially asconcerns particular characteristics and features thereof which willbecome apparent as the specification continues.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of the composite web of the presentinvention depicting unidirectionally oriented fibers in one layer andrandom fibers in an adjoining layer.

FIG. 1A is a schematic sectional view depicting a pair of tapes eachhaving unidirectionally oriented fibers which are at different angles.

FIG. 2 is schematic sectional view depicting multiple layers each havingunidirectionally oriented fibers in different directions.

FIG. 3 is a schematic view showing the process for manufacturing thecomposite web depicted in FIG. 1 with a portion enlarged and in sectionto emphasize layering relationships.

FIG. 4 is a side elevational view of an apparatus employed to make ahoneycomb core from the composite web of the present invention.

FIG. 5 is an enlarged sectional view of a portion of FIG. 4 showing atleast one mandrel employed in the apparatus of FIG. 4.

FIG. 6 is an enlarged sectional view of a portion of FIG. 4 emphasizingadjacent composite tapes or webs employed in the formation of ahoneycomb structure.

FIG. 6A is an enlarged sectional view of a typical trio of mandrelsrepresenting radiused corner portions of the same.

FIG. 7 is a schematic isometric view depicting the orientation of theunidirectional fibers in a honeycomb block built with the apparatus ofFIG. 4 and showing the conventional orientation nomenclature.

FIG. 8 is a partial side elevational view of a honeycomb structureformed by composite material of the present invention sandwiched to afacing to form a panel.

For a better understanding of the invention reference is made to thefollowing detailed description of the preferred embodiments thereofwhich should be referenced to the hereinabove described drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various aspects of the invention revealed in the following detaileddescription of the preferred embodiments which should be taken inconjunction with the prior described drawings.

The invention as a whole is depicted in the drawings by referencecharacter 10. The composite web or tape 10 includes as one of itselements a first layer 12 of material including a plurality ofstructural fibers 14 arranged to lie substantially unidirectionallywithin layer 10. Each of the plurality of fibers 14 in the presentembodiment measures 5 to 25 microns in diameter. The overall thicknessof layer 12 is approximately 25 microns and is considered to be "thin"in the field of composite structures. In general, a thickness of a webor tape less than 40 microns is considered to be "thin". Layer 12, asdepicted in the drawings is approximately 15 microns in thickness. Thistranslates into a Fiber Areal Weight (FAW) of less than 45 gms/m². Theplurality of fibers 14 may be Aramid fibers, carbon fibers (having anelastic Modulus as high as one hundred thirty million psi), polyethyleneterapthalate fibers, and many other high performance structural fibers.It should be noted that it is known that there is good electrical andheat conduction along plurality of fibers 14 when ultra high moduluscarbon fibers are employed, having a modulus of greater than 75 millionpsi. Carbon fibers generally have a negative coefficient of thermal ofexpansion along the length of plurality of fibers 14. However, by mixinga variety of fibers, such as different carbon fibers, within first layer12, the coefficient of thermal expansion can be rendered at about zero.Of course, substituting lower modulus carbon fibers or other fibers forcarbon fibers would result in a positive thermal coefficient ofexpansion to varying degrees. The plurality of fibers 14 may becontinuous or plied in structure, depending on the tow employed in itsmanufacture. A unidirectional tape pre-impregnated with a resin of thetype depicted as first layer 12 is available under the designation XN50A/RS-3, FAW 20 gm/m², resin %=53±3, from Y.L.A. Inc. in Benicia,Calif.

Adjacent first thin layer 12 is second thin layer 16 which includes aplurality of structural fibers 14, depicted in FIG. 1, in randomconfiguration. Plurality of random fibers 18 may be composed ofstructural fibers such as those recited in conjunction with first layer12. However, the fibers in second layer 16 may be the same or differentthan the fibers used in first layer 12. The width of second layer 16 inthe embodiment described is approximately 15 microns.

Resin matrix 20 transfers the load from one fiber to the next withinplurality of fibers 14 and 18. In addition, resin matrix 20 serves tocontain plurality of fibers 14 and 18, and to connect first and secondlayers 12 and 16 together within web structure 10. In the formation ofweb structure 10, resin matrix 20 initially found in first layer 12,flows into layer 14 by the application of heat. On the other hand, resin20 may initially be used in the second layer 16 and be caused to flow inthe opposite direction toward the first layer 12. Resin matrix 20 may becomposed of any of the polymers of epoxy, polycyanate, bismaleimide andthe like. When plurality of fibers 14 and 18 are carbon fibers, apolycyanate resin suffices in this regard. For example, a toughenedpolycyanate resin designated RS-3 and sold by Y.L.A. Inc. of Benicia,Calif. may be used. Release papers 24 and 26 protect composite structure22 and facilitate the handling of the same. Of course, release papers 24and 26 are removed prior to use of web structure 10, which will bedescribed hereinafter. FIG. 1A depicts a web 10A having first and secondlayers 12A and 14A, each composed of unidirectional fibers which areoriented at 90 degrees to one another.

With reference to FIG. 2, it may be observed that composite web 10B isdescribed utilizing a mat layer 28 and unidirectional layers 30, 32, and34. Of course, a resin matrix, such as resin matrix 20, is employed inweb structure 10B to bind the four layers together and carry the loadfrom one fiber to the next. It should be noted that unidirectional layer30 possesses fibers oriented along unidirectional arrow 36. In contrast,layer 32 includes unidirectional fibers oriented perpendicularly to theplane of the drawing page, ie: orthogonally relative to the direction ofunidirectional fibers in layer 30, denoted by a multiplicity of "x's".Finally, layer 34 includes unidirectional fibers at approximately 45degrees to the unidirectional fibers found in layers 30 and 32,directional arrow 33.

With reference to FIG. 3, it may be seen that composite web 10B may beformed by bringing together tapes 40 and 42. Tape 40 consists of layers28 and 30 while tape 42 includes unidirectional layers 32 and 34. Thetapes 40 and 42 pass through a pair of hot nip rollers 44 and 46 whichinitiate the flow of resin between tapes 40 and 42 to fuse or connectthe same at interface 50, FIGS. 2 and 3. The fused tapes 40 and 42 passover guide roller 48 and onto chill plate 50 which stabilizes the flowof the resin matrix within composite web 10B. Guide roller 52 directscomposite web 10B onto takeup roller 54 for use. It should be noted thatcomposite web 10B may also include release papers such as release paperlayers 24 and 26 shown with respect to composite web 10.

Referring now to FIGS. 4-6, composite web 10 may be formed into ahoneycomb, such as that depicted by honeycomb 56 in FIG. 7, for use inpanel structures such as panel 58 depicted in FIG. 8. Turning now toFIG. 4 apparatus 59 is depicted for producing honeycomb core 56.Apparatus 59 utilizes a base plate 60 having a bottom surface 62 whichrests on a platform or ground supported structure. The base plate alsoincludes an upper surface 64 which may be coated by a non-stick materialsuch as Teflon. Base plate surface 64 is formed with a plurality ofpeaks and valleys, or other contours, determining the cell shape andsize of the core to be manufactured. In the embodiment shown in FIG. 4,upper surface 64 possesses an angular configuration of half of the formof a right regular hexagon. Fence 68 is movable according to directionalarrow 70 and determines the length of the honeycomb structure 56 to bemanufactured. A first web or tape 72, which may comprise the compositestructure 10, is placed across upper surface 64 of base 60, beginning atfixed fence 74 and extending to movable fence 68. Plates 76 and 78attach to fences 70 and 74, respectively, and determine the height ofthe block or core 56 to be constructed. It should be observed that theunidirectional fibers of composite structure 10 are orientedperpendicular to the page of the drawings in FIG. 4.

A plurality of mandrels 80 are laid in the recesses along surface 64 ofbase plate 60. Each mandrel such as mandrel 82, FIG. 5, accommodates thethickness of composite tape 72 which is pressed beneath mandrel 82, andis sized to determine the cell size of honeycomb core 56. Plurality ofmandrels 80 are formed of heat conducting material such as aluminum,titanium, steel and the like. Each mandrel of plurality of mandrels 80may be coated with a layer 84 of non-sticking material such as Teflon,shown with respect to mandrel 86 on FIG. 6. Second tape 88, FIG. 4, isthen placed over the first row of mandrels occupying the valleys orrecesses found in upper surface 64 of plate 60. Tape 88 may have thesame structure as tape 72. Plurality of mandrels 80 would includemandrels such as mandrel 86 that overlies the top of tape 88, thus,pressing tapes 72 and 88 together at peak 90, FIG. 6 of upper surface 64or at the top of another mandrel of plurality of mandrels 80. It shouldbe observed that adhesive 92 can be placed between tapes 72 and 88 incertain types of cores requiring adhesion at this point, FIG. 6. Trio ofunexpanded mandrels 81, 83, and 85, FIG. 6A each include radiused orcurved corners 87, 89, and 91 which permit the high modulus fiberswithin the webs or tapes 100 and 102 to accumulate in the void 104 atthe intersection of mandrels 81, 83 and 85. Bends 106 and 108 of tapes100 and 102 represent such accumulation. This accumulation prevents theformation of wrinkles in the webs 100 and 102 which weakens the eventualhoneycomb structure 56. Also, such radiused corners allow closeconformance of the fibers to the corner of each mandrel without breakageof such fibers, thereat.

Vacuum bag 94, FIG. 4, is then placed over the built-up structureconstituting a plurality of tapes 96 and a plurality of mandrels 80 to aheight of the desired width of finished core 56. Pressure may also beapplied by clamping the assembled tapes, and mandrels together andheating this clamped assembly such that the mandrels, expanding with theapplication of heat, exert the necessary pressure on the plurality oftapes 90. A negative pressure of between 8 and 14 psig is applied tovacuum bag 94 and the entire apparatus structure 59, plurality of tapes96, and plurality of mandrels 80 is placed in an oven for several hoursat a curing temperature appropriate to the resin 20 used. The structureof FIG. 4 is then removed from the oven and allowed to cool down to roomtemperature. Plurality of mandrels 80 are then removed leaving theconstructed honeycomb core 56. Further cooling may be necessary toachieve complete separation of mandrels 80 from core 56. Additionalresin may be dip coated on the surface of honeycomb core 56, asnecessary followed by additional heat curing. With reference to FIG. 7,it should be noted that "W", "T", and "L" refer to the width, thicknessand length dimensions of core 56, respectively. It should be realized,that the orientation of the unidirectional fibers in this example arealigned in the thickness direction ("T") shown by representative patch98. A sandwich facing 100 may be applied to each side of honeycomb core56 to form a panel 58 as shown in FIG. 8. The thickness dimension isalso depicted in FIG. 8 for the sake of clarity.

The following examples are presented to further detail the inventionsought for patenting, but should not be deemed to be restrictive of suchinvention:

EXAMPLE I

Employing apparatus 59, depicted in FIG. 4, honeycomb blocks wereconstructed utilizing the composite web depicted in FIG. 1 consisting ofa first layer of a unidirectional tape, 33 grams FAW, 50-55% resin,XN-50A pitch carbon fiber, 75 mpsi modulus, available from Y.L.A. ofBenecia, Calif. The second layer included a random mat of carbon fiber8000015, 100% PAN based carbon of the type available from InternationalPaper Co. of Tuxedo N.Y. Blocks were also constructed with the randommat second layer alone, 17 gram FAW, available from the same source.Apparatus 59 and the uncured blocks were placed in vacuum bag 94 under anegative pressure. The blocks were heated at 350° F. for (3) hours in anoven, removed, and allowed to cool down to room temperature overnight.After removing the mandrels following cool down, the blocks constructedof the composite web 10 of FIG. 1 and radom mat alone were trimmed witha circular saw, weighed, and measured to determine density. Thefollowing table represents density measurements of identified blocksprepared according to Example I without subsequent resin dip treatment:

                  TABLE 1                                                         ______________________________________                                                             DENSITY                                                  BLOCK                (pounds per cubic foot)                                  ______________________________________                                        1.  RS-3 Resin System, first ply                                                                       1.2                                                      of 33 gm FAW of XN-50A (Nippon                                                Petro Chem) at 0°; second ply                                          of 17 FAW 33 mm CF at random                                                  orientation (Int Paper)                                                   2.  RS-3 Resin System, first ply                                                                       1.0                                                      of 25 gm FAW of T-300 (Toray)                                                 at 0°; second ply of 17 FAW,                                           33 mm CF at random orientation                                                (Int. Paper)                                                              3.  RS-3 Resin System, one ply                                                                         0.5                                                      only of 17 FAW, 33 mm CF                                                      33 mm at random orientation                                                   (Int. Paper)                                                              4.  RS-3 Resin System, first ply of                                                                    0.8                                                      10 gm FAW of T-300 (Toray) at 0°;                                      second ply of 17 FAW, 33 mm CF                                                at random configuration                                                   ______________________________________                                    

The blocks of Table 1 were treated using a solution of 10% RS-3 resinand 90% methylethylketone. After removal from the solution, the blockswere cured in an oven at 350 degrees fahrenheit for three hours, cooled,and reweighed.

The following table represents the density measurements of the blocks.

                  TABLE 2                                                         ______________________________________                                                             DENSITY                                                  BLOCK                (pounds per cubic foot)                                  ______________________________________                                        1.  RS-3 Resin System, first ply                                                                       1.3                                                      of 33 gm FAW of XN-50A (Nippon                                                Petro Chem) at 0°; second ply                                          of 17 FAW 33 mm CF at random                                                  orientation (Int Paper)                                                   2.  RS-3 Resin System, first ply                                                                       1.1                                                      of 25 gm FAW of T-300 (Toray)                                                 at 0°; second ply of 17 FAW,                                           33 mm CF at random orientation                                                (Int. Paper)                                                              3.  RS-3 Resin System, one ply                                                                         0.6                                                      only of 17 FAW, 33 mm CF                                                      at random orientation                                                         (Int. Paper)                                                              4.  RS-3 Resin System, first ply of                                                                    .85                                                      10 gm FAW of T-300 (Toray) at 0°;                                      second ply of 17 FAW, 33 mm CF                                                at random configuration                                                   ______________________________________                                    

As may be observed, each block added approximately 0.1 pound per cubicfoot to its density measurement by this dipping and curing process.

Preliminary compressive strength tests indicates that blocks 1 and 2 ofTables 1 and 2 exhibits substantially highly compressive strength over 1lb. aluminum honeycombs currently available in satellite structures.

While in foregoing, embodiments of the present invention have been setforth in considerable detail for the purposes of making a completedisclosure of the invention, it may may be made in such detail withoutdeparting from the spirit and principles of the invention.

What is claimed is:
 1. A composite honeycomb core structurecomprising:a. a first layer of material containing a plurality ofstructural fibers arranged to lie substantially unidirectionally withinsaid layer; b. a second layer material positioned adjacent said firstlayer, said second layer containing a plurality of structural fibers ineither random or unidirectional configuration; c. an impregnatingmaterial for forming a matrix connecting said first and second layersbinding said fibers within said first and second layers, said first, andsecond, layers being formed into a honeycomb core, said first and secondfiber-containing layers of material forming the cell walls of saidhoneycomb core having a density of less than 2.0 pounds per cubic foot.2. The composite web structure of claim 1 in which said plurality offibers within said first layer are carbon fibers.
 3. The compositestructure of claim 2 in which said plurality of fibers within saidsecond layer are carbon fibers in random orientation.